Topographical models of geographical areas may be used for many applications, including flight simulators and flood plain analysis. Furthermore, topographical models of man-made structures (e.g., cities) may be extremely helpful in applications such as cellular antenna placement, urban planning, disaster preparedness and analysis, and mapping, for example.
Various types and methods for making topographical models are presently being used. One common topographical model is the digital elevation model (DEM). A DEM is a sampled matrix representation of a geographical area which may be generated in an automated fashion by a computer. In a DEM, coordinate points are made to correspond with a height value. DEMs are typically used for modeling terrain where the transitions between different elevations (e.g., valleys, mountains, etc.) are generally smooth from one to a next. That is, DEMs typically model terrain as a plurality of curved surfaces and any discontinuities therebetween are thus “smoothed” over. For this reason, DEMs generally are not well suited for modeling man-made structures, such as skyscrapers in a downtown area, with sufficient accuracy for many of the above applications.
U.S. Pat. No. 6,654,690 to Rahmes et al. discloses a significant advance in topography. The '690 patent discloses an automated method for making a topographical model of an area including terrain and buildings thereon based upon randomly spaced data of elevation versus position. The '690 patent is assigned to the assignee of the present invention and is incorporated herein by reference in its entirety. The method includes processing the randomly spaced data to generate gridded data of elevation versus position conforming to a predetermined position grid, processing the gridded data to distinguish building data from terrain data, and performing polygon extraction for the building data to make the topographical model of the area including terrain and buildings thereon.
In particular, a terrain-only DEM is generated and a building-only DEM is generated. Once the buildings have been distinguished from the terrain, polygon extraction is performed for the building data. The '690 patent makes a typographical model of the area including terrain and buildings thereon in a relatively quick manner and with enhanced accuracy. Nonetheless, what generally happens is that much of the foliage, and in particular trees, may be treated as buildings. That is, polygon extraction is also performed on the data representing the trees. This results in a large number of polygons being used to model a tree as compared to the number of polygons used to model a building. When the topographical model is displayed on a viewer, the modeled foliage is not very realistic looking. Consequently, the modeled foliage is manually removed and replaced with a more realistic model. This may be relatively time consuming and labor intensive.